Thermoeconomic modeling and exergy analysis of a decentralized liquefied natural gas-fueled combined-cooling-heating-and-power plant

A small-scale combined-cooling-heating-and-power (CCHP) plant is proposed as a possible alternative to large-scale, centralized, electricity-only power plants. The proposed system is based on a non-ideal gas turbine (Brayton) cycle, integrated with a cooling plant and a district energy network. The study analyzes whether the proposed system could be an ideal candidate for distributed generation applications, especially in locations which are distant from centralized power plants. Therefore apart from reducing transmission and distribution losses, waste heat could be recovered effectively to generate heating, or cooling (via a cooling plant based on absorption refrigeration technology). The system considers fueling with liquefied natural gas (LNG), which is a safe and transportable fuel option. The cooling energy in the LNG is recovered in a useful manner since LNG regasification is coupled to the ambient air feed to the air compressor. The study includes a basic thermodynamic analysis, followed by an exergy analysis and a cost analysis. The simulation results signify a potential for further investigation of the proposed system, since its performance results in significant thermodynamic and environmental improvements, when compared to an equivalent conventional system. The system operates in two modes: (a) winter operation, where recovered heat is distributed to the district energy network, (b) summer operation, where recovered heat is used to drive an absorption chiller cooling plant to generate cooling, which is also distributed to the district energy network. The average primary energy ratio of the proposed system is 0.91, while the net electrical efficiency is 0.356 and 0.365, for summer and winter operation, respectively. The average exergetic efficiency is 0.419, which is a 25% improvement when compared to the conventional system. The cost analysis shows that the payback period is within a reasonable time frame (approximately 4 years), for a total initial cost of 17.1 million €.